This application claims priority from and incorporates by reference U.S. Provisional application Ser. No. 60/276,780, filed Mar. 16, 2001 and U.S. Provisional application Ser. No. 60/314,859, filed Aug. 24, 2001.
The present invention relates to tubes in chemical reactors, and, in particular, to a device and method for measuring the back pressure in the tubes and for blowing dust out of the tubes.
Many chemical reactors use a catalyst as part of the reaction process. The catalyst material frequently is coated onto or contained in a substrate which is packed in tubes within the reactor. The reactants flow through the tubes and out the open ends of the tubes, reacting in the presence of the catalyst to form the products of the reaction. It is desirable to be able to measure the packing of catalyst within the tube in order to determine whether the tube will function properly. Ideally, the catalyst packing in all the tubes will be very close to the same. However, in reality, there is a variation in packings which adversely affects the efficiency of the reaction by providing for different residence times in different tubes.
In order to assess the catalyst packing, a constant flow rate test gas is injected into the tubes, and the back pressure is measured, with the back pressure being proportional to the packing density. Higher densities produce higher back pressures, and lower densities produce lower back pressures. High back pressures can also indicate problems other than high packing density, such as dust, fines, obstructions in tubes, and the presence of foreign material. Low back pressures can also indicate problems other than low packing density, such as bridging. The goal is to measure the back pressure on each tube and determine which tubes require corrective action. Then, once the appropriate corrective action has been taken, the corrected tubes can be retested.
Measurements may be taken when the tubes are first loaded with catalyst, in order to ensure that they are properly loaded, as well as periodically during the operation of the reactor, such as during normal maintenance shut-downs, and after cleaning. However, the devices and methods that have been used in the past have been labor intensive and time consuming, their accuracy has depended largely upon the skill of the operator, and they have yielded data that is not readily usable.
In order to obtain a seal between the test device and the chemical reactor tube, the operator has typically inserted a stopper into the tube. Weldments at the top of the tube can interfere with the ability to obtain a good seal, and failure of the operator to maintain the device in a vertical orientation may also interfere with the ability to obtain a good seal. The operator typically must keep track of his position manually, and the data that is obtained is typically written down on a notepad by a second person, sometimes with the person who takes the measurements shouting over the noise of the plant to the person writing down the results. Also, the tubes are typically measured one at a time, requiring many workers and a long shut-down time. With typical prior art methods, it is difficult to keep track of all the measurements, since there may be as many as 35,000 tubes to be measured in a reactor, and transferring data from the many notepads is slow and provides an opportunity for errors. In order to display the progress of the measurement process, the operators usually put colored caps on the tubes as they are measured, which is time-consuming.
The present invention provides a device and method that improves the ability to measure the back pressure in tubes, making the process much more accurate, faster, less labor intensive, more efficient, safer, less dependent on the skill of the worker, and yielding more accurate and more useful results. In a preferred embodiment, the measuring device uses an inflatable, conforming seal, which provides a good seal between the measuring device and the chemical reactor tubes. Also, in a preferred embodiment, the measuring device measures multiple tubes at once rather than measuring only one tube at a time. Also, in a preferred embodiment, measurements are stored at the measuring device, are transmitted electronically to a remote computer, and are displayed graphically in real time at a remote display, such as in the control room, including indications of which tubes are within predetermined specifications and which are not.
The visual display helps the plant engineer determine which tubes require corrective action and may permit the elimination of the time-consuming prior art process of putting caps on all the tubes as the measurements are being taken.
Preferred embodiments of the present invention also permit automated handling of the data and prompt statistical analysis and cost-effectiveness analysis of the measurement data in order to help the plant engineer make quick decisions about corrective actions to be taken. The measurements that have been taken with a prototype device made in accordance with the present invention are so accurate that the engineers can begin to recognize what particular variations in pressure drops meanxe2x80x94for example, one pressure drop indicates that a foam pig accidentally has been left in the tube after cleaning, while another indicates that an extra clip has been inserted to retain the catalyst. In addition, in a preferred embodiment of the invention, a device and method are provided to remove dust from the tubes by blowing gas through them.
The gas used in the preferred embodiments as described herein may be air, nitrogen, or some other gas.